Telephone system



Jan. 11, 1938. R6. DIXON 2,104,975

TELEPHONE SYSTEM Filed Nov. 9, 1935 3 Sheets-Sheet 1 I, I (/1) -I if 5EEE F M 2/ f m/ I IV I 2130 :Dvvexvrok- R. G. DIXON TELEPHONE SYSTEMJan. 11, 1938.

s Sheets-Shet 2 Filed NOV. 9, 1935 l jS/P Patented Jan. 11, was2,104,975

g'E'iS ATENT OFFICE TELEPHONE SYSTEM Reginald Griffith Dixon, ElthamPark, London,

England, assignor to Siemens Brothers 8; Company Limited, London,England Application November 9, 1935, Serial No. 49,003 In Great BritainNovember 14, 1934:

4 Claims. (01. 179-18) The present invention relates to telephone sys-In order to overcome the restriction placed on tems and moreparticularly to systems in which the number of outlets per group of theallotter by common apparatus is called into use temporarily providing aseparate stopping or last contact to aid in the setting up of aconnection. position for each group to cater for the all out- In asystem in which temporary use is made lets busy condition it is arrangedthat the busy 5 of common apparatus it is important that such signallingcondition is brought about when the apparatus should be released as soonas possible common apparatus tests the last finder in a after it hasfulfilled its purpose. If such appamarked group 'if this finder and theremainder ratus includes a searching device the release of of thefinders of the group are busy. Such an the apparatus is liable to delayif the search has arrangement may be carried out by preparing 10 beenunsuccessful and the release is under the the circuit of a relay whenthe first finder of the control of a subscriber or operator who has togroup is tested and operating the relay when the be given a busy signalconsequent on the unsuclast finder of the marked group is reached andcessful search, or if the release is brought about if the search hasbeen unsuccessful the operation by a slow acting time limit device. ofthe relay in conjunction with the non-opera- 15 In the present inventionarrangements are protion of the test relay brings about the release ofvided in a system employing backwardly hunting the allotter and thetransmission of the signal switches, hereinafter referred to as finderto a preceding circuit to bring about the transswitches, in theconversational path which are mission therefrom of a busy signal. Thesigtaken into use by temporarily used common apnalling circuit to thepreceding circuit may in- 20 paratus wherein, if on the demand arisingno elude a wiper of the allotter and the circuit over free finder switchis available the common apwhich the common apparatus is taken into use.paratus is immediately released. It is a iea For the simplification ofthe starting arrangeture of the invention that the release is effectedments where a plurality of homing allotters is by removing the startingcondition which caused available to a calling circuit and to minimizede- 25 the common apparatus to be taken into use. lay when a number ofcalls are present simul- According to a further feature of the inventiontaneously it may be arranged to start up more when no free finder switchis available a signal than one allotter to search for a free call finderis transmitted from the common apparatus to and for the prevention ofdouble seizure by ala preceding circuit which brings about the relottersthe starting arrangements are such that 30 moval of the starting signaland may bring about allotters are started in succession after a delaythe transmission from the preceding circuit of a period, the delayperiod providing for the dis busy signal. The common apparatus may serveabling of a further allotter after a call finder a plurality of groupsof finders the group to be has been seized. Cross connections betweenal- 5 searched. being determined by marking applied lotters may beprovided such that the first to find by a relay responsive to thestarting signal. The a free call finder creates an artificial busyconcommon apparatus may take the form of an aldition so far as theremaining allotters are conlotter comprising a hunting switch andcontrol cerned, it being arranged that the delay in startcircuitstherefor and arrangements may be proing an allotter is not less than thetime taken vided whereby it'is ensured that the whole of a after thefinding of a free call finder to apply the 4 desired group of finderswitches is searched beartificial busy condition. fore the signal to thepreceding circuit to bring An embodiment of the invention is shown byabout the release of the allotter is transmitted. way of example in theaccompanying drawings This is of importance in the case of homing typewhich will now be referred to.

switches where two or more switches are started Fig. 1 shows a cordcircuit to which access is 45 in response to a starting signal since agroup may had over call finders, Fig. 2 shows in the upper be marked inresponse to a starting signal after part a jack circuit and a jackfinder associated the hunting switch has entered it. In order to with aP. B. X. line, while Fig. 3 shows in the ensure that the whole of amarked group is upper part the line circuit of a P. B. X. line. In

searched before the allotter can be released it is the lower part ofFigs. 2 and 3 is shown a homing arranged that the signal to be givenwhen the type allotter for allotting a jack finder associated huntingswitch has tested the last finder of a with a free P. B. X. line whenrequired.

group and has found it engaged is dependent on The operation of the cordcircuit shown in the prior receipt of a signal indicative of the factFig. 1 will now be described. The circuit tests that the first finder ofthat group has been tested. free to an allotter for allotting a callfinder to 55 contact 7'6 to lamp deal with the call by reason of thebattery connection to wire P over contact 1225. When the connection tothe cord circuit is switched through by the call finder, relay Loperates over the calling loop, the earth connection being over contacts7'5, f6 and n6. Contact ll closes a circuit for relay B. Relay Boperates and at contact bl connects earth to wire P to mark the circuitengaged and at contact b5 connects earth over AL which serves as acalling supervisory lamp. Lamp AL lights up. Contact b4 connects earthover windings (I) of relays N and M in the plug sleeve circuit. Theoperators instrument is connected to the calling line over contacts m2and m3 and the operator ascertains the callers requirements. She theninserts the plug CP into an appropriate jack. If the called line isfree, operation of the cut on" relay applies battery potential over alow resistance to the bush of the jack and relay N is operated. Thisrelay locks up by means of its winding (II) over contacts nl, f5 and b2and at contact 125 connects earth directly to the plug sleeve to engagethe line and short circuits its winding (I) and winding (I) of relay Mand completes a'circuit for the latter relay to operate on its winding(II). Relay M is differentially wound. When a plug is removed from theshelf, contacts PSC close and relay M having operated, a locking circuitis closed over winding (III) of the relay, contacts ml and PSC. Contact121.! opens the operating circuit for relay M. Contacts m2 and m3disconnect the operators instrument circuit from the cord circuit,contact 1124 closes a circuit for the called supervisory lamp CL overcontact d2, contact m5 disconnects the battery potential signifying afree cord circuit from wire P and contact m6 closes an operating circuitfor relay J over contact b2. Relay N having operated, the tip and ringconductors of the plug are connected up over contacts n2 and n3 and aleak circuit to enable the caller to hear ringing signal is closed atcontact 124. The circuit over the busy tone lead BS is disconnected atcontact 126 before relay J operates, and earth is connected directly torelay L. On the operation of relay J contact y'l substantiates contactbl, contacts '2 and i3 apply ringing current over leads RC to the calledline, contact '4 closes a point in the metering circuit over wire MP,and contact 7'6 extinguishes the lamp AL leaving this now dependent onrelay L for further illumination. When the called subscriber replies tothe ring, relay F operates lamp and calling by means or" its winding (I)over the called loop in known manner and locks up over its winding (II),contacts fl and PSC. Contacts f2 and f3 disconnect the ringing leadsfrom the plug and connect the called line to the feeding bridge andrelay D operates over the called subscribers loop. Contact f4 closes afurther point in the metering circuit, contact f5 changes over to hold(II) and contact 5 and contact d2 extinguishes lamp CL. The calling andcalled parties are now in communication with one another.

At the end of the conversation the supervisory lamps are lit as eachsubscriber clears. caller is the first to clear, relay L releases and atcontact Z2 completes a circuit over contact m4 for lamp AL. Contact llreleases relay B which releases relay J at contact b2 and at contact b3closes the metering circuit. The call is metered during the slow releaseof relay J by the application to wire MW of suitable potential connectedto wire MP. Contact b5 opens to guard against continued glowing of lampAL after the release of relay J and contact b -l opens in the operatingcircuit for *elay N. The busy marking is removed from the cord circuitat contacts bl and il but the battery potential indicating a freecondition remains unapplied to wire P since relay M is still operated.When the called party clears, relay D releases and at contact dl opensthe holding circuit for relay N and at contact 0Z2 completes the circuitforlamp CL. Release of relay N disconnects the plug from the cordcircuit. The operator seeing both lamps glowing withdraws the plug fromthe jack and on the restoration of the plug to the shelf, contact PSCopens and relays F and M are released. Contacts m2 and m3 re-connect theleads to the operators instrument circuit and contact 1124 extinguishesthe supervisory lamps.

If the wanted line were one connectable to the jack over a finderswitch, there would be no indication of its condition at the time ofplugging into the jack; consequently if the line was busy there would beno indication of this until its condition had been ascertained byapparatus associated with the finder switch. Arrangements of this natureare shown in Figs. 2 and 3 and will be'fully described hereafter.Immediately the plug is inserted into the jack relay N will not beoperated owing to the'resistance connected between battery and the bushof the jack; If a busy condition is encountered earth will be connectedin subsequent apparatus to lead BS is not interrupted. Relay M locks upand brings about the operation of relay J but relay F is not operated.Consequently busy tone is transmitted to the caller over lead BS,contacts 7'5, f5, and at. The connection is taken down when the callerclears as both supervisory lamps will now be glowing.

The system is one in which metering takes place, even though the calledsubscriber fails to n! and back contact it. 7

If the jack of the wanted line is already plugged the operator willinsert the plug into a special busying jack the bush of Relay M will beoperated and busy tone transmitted to the caller in the manner abovedescribed.

The complete operation of the circuits shown is described in theapplication of William G. Patterson and Reginald G. Dixon, Serial No.48,952, filed Nov. 9, 1935, only those parts of the cord circuit andtheir operation being shown herein as are necessary for theunderstanding of the present invention;

The jack CJ shown on the left of Fig. 2 to which reference will now behad may be considered as one in which an operator may insert the plug SFof Fig. 1. The finder JF is one of a number multipled to a group ofjacks which serve the lines of a P. B. X. group. There may be 100 linesin the multiple distributed over a number of P. B. X. groups. Each jackfinder is connected to one line of a group which is shown in Fig. 3 atSUB together with the line circuit of that line denoted which will beearthed.

by the single step line and cut off relays LC and KC respectively.

The jack finders of a number of P. B. X. groups are multipled in thebanks of two allotters, one allotter FA being shown in the lower part ofFigs. 2 and 3. The allotters are outlet switches and the jack finders100 outlet switches, both being of the high speed motor driven type.

Associated with jack CJ is a sleeve relay S and a cut off relay CO. Thejack finder motor is designated JFlVl and is represented as a magnet andthe allotter motor FAM is similarly shown but the actual driving deviceis an electric motor the circuit of which is controlled by a latchmagnet which also withdraws from and inserts into the riving mechanism alatch, the engagement of the latch with the mechanism bringing theswitch to rest immediately on operation of the test relay. The testrelay for the finder JF is situated in the allotter circuit and isdesignated K, that for the allotter being designated C. H is theswitching relay. The start relay is designated CS and a pair of relaysSA and SB are associated with two allotters for closing the startingcircuits of the allotter in which relay A issituated. Relay SB isheavily slugged to retard its operation by 100 to 200 milliseconds afterthe operation of relay SA.

The terminals designated AT are commoned and connected in groups tocontact $2 of sleeve relay S of the jacks concerned with a P. B. X.group. These terminals are cross connected in groups to terminals CTcorresponding to positions on the allotter bank connected to jackfinders of a group, the terminals of a group in CT being commoned. Theterminals DT are also connected in groups to contacts in the allotterbank corresponding to jack finders of a group. Of these contacts thosecorresponding to the first and last lines of a group are cross connectedto the corresponding commoned contacts in set AT. Terminals BT arecommoned similarly to terminals AT and are connected to contacts s4 ofthe jack circuits. They are connected to the contact in the group ofterminals ET corresponding to the last contact associated with a groupof jack finders in the allotter bank. The terminals FT are commoned ingroup and connected to contacts in both allotter banks corresponding tojack finders. Terminals GT are similarly commoned. Relays SS and ZZ areconcerned with the forced release of an allotter if it is held beyond apredetermined time. The allotter shown may be considered as the firstallotter to be started on receipt of a start signal, the startingcircuit being shown in chain dotted lines while the starting circuit forthe later allotter to be started is shown in dotted line. The rectifierR2 prevents operation of relays C, E and G through the commoning ofterminals AT by earth connected over wiper FAT.

The operation of the circuits is as follows: When a plug is insertedinto jack CJ, relay S which is of high resistance is operated but relaysM and N in the cord circuit do not operate. Contact sl connects earth tostart relay CS, contact 82 connects earth to the commoned terminals AT,contact s3 connects the right hand winding of relay CO to the jackfinder test bank contact and contact s l connects the bush of the jackto the commoned terminals BT. Relay CS operates and at contact cs!closes the following circuit: earth over the dotted line connection, offnormal contacts on? of the first allotter FA, the common point SC, ofinormal contacts corresponding to 011.2 of the second allotter, the chainline connection, contact 031, relay 'SA to battery. Relay SA operatesand at contact sal connects earth over the dotted line connection normalcontact wiper FA8 of the allotter, contacts 224 and D4 to relay A.Contact sa2 connects earth to the common point SC to hold relay SA afterthe allotter moves from normal and contact sa3 closes the circuit forrelay SB. Relay A operates in the above traced circuit over wiper FABand locks up over contacts 12, al and 032. Contact 122 closes thecircuit for relay B over contacts ll, i2 and 222. Relay B operates andat contact bl closes the circuit for the allotter driving device. Thiscircuit runs from earth over contacts bi, cl, g1, i3, dl, motor FAM tobattery. Contact 222 opens a point in the homing circuit for theallotter, contact 193 closes a point in a circuit which includes wiperFAQ to be completed if no free jack finder is available, contact 114opens the operating circuit of relay A and prepares a circuit to bedescribed hereinafter to prevent the testing-in and to bring about thehorning of the second allotter, contacts b5 and b5 prepare circuits forrelay SS to be described later and contact bl connects battery over highspeed relay E and back contact fi to wiper FAT. The motor FAM starts anddrives the allotter in search of a free P. B. X. line in the requiredgroup. The testing circuit includes wiper FAG the contacts in the arc ofwhich corresponding to the required group are marked over terminals CTand AT by contact 52 and runs from earth over contact 82, terminals AT,CT, wiper FAG, rectifier RI, contact i i, test relay C which is of thehigh speed type, wiper FA5, contact 104, contact kc l, resistance tobattery. When the allotter reaches the first contact of the requiredgroup, high speed relay E is operated in the following circuit, earthover contact 82, terminals AT, DT, contact corresponding to first linein the group in the contact arc of wiper FAT, wiper FAT, back contactfl, rectifier R2, contact bl, relay E to battery. Contact el closes andconnects high speed relay F to the back of contact fl but the relayremains short circuited until the switch leaves the contact over whichrelay E operated. If and when this occurs, relay F operates in serieswith relay E and changes over its contact 1 l to connect high speedrelay G to wiper FAT. If a free line is found relay C operates in theabove traced circuit and at contact cl opens the driving circuit andcloses a circuit for relay D. Relays KC and LC operate on their windings(I) and earth over relay C and wiper FA5 is extended over contacts 7603and Z03 to the test wire in the line finder multiple over which outgoingcalls are made. The windings (II) of relays LC and KC are disconnectedfrom the line SUB at contacts 20!, Z02, kcl, 7002 and contact 7004removes the non-inductive shunt from the windings (I) The allotter isbrought to rest and a further point in the driving circuit is opened atcontact d! on the operation of relay D. Contact d2 connects earth overcontacts M, .224 to wiper FA8 the contacts in the arc of which arecommon in groups so that the earth potential is extended over thecommoning and wiper FAvZ of the other allotter when it is rotating overcontacts of the group, contacts 224, D4, and back contact d2 thereof toits wiper FA5 to mark the lines of the group engaged to the otherallotter and prevent its testing in. Contact 023 connects the jackfinder test relay K to wiper FA! and contact (Z4 connects earth overcontact ki and wiper FA2 to the driving device JFM of the jack finder.Contact (15 connects earth to wiper FAQ which extends it over commonedterminals GT multipled over both allotters, wiper'FAS of the secondallotter, back contacts 75 and (15 thereof to the junction of relay Eand the resistance to prevent the initiation of the busy testingarrangements. The motor JFM of the first allotter is started and thejack finder connected to the line seized by the allotter moves off insearch of the plugged jack. When this is found, relay K operates in thefollowing circuit, earth over high speed test relay K, contact d3, wiperFAI, and contact connected to wiper JF4, contacts corresponding to thegroup concerned in the wiper arc cross-connected to terminal MT, WiperJF3, contacts 83, col, resistance to battery. Relay CO operates afterrelay K has operated and holds temporarily in series with it overcontact col. Contact 002 disconnects relay S andconnects the left handwinding of relay CO to the bush of the jack. This winding being ofconsiderablylower resistance than that of relay S permits relay N in thecord circuit to operate with results already described in connectionwith ,Fig. 1. Relay K operating, contact kl opens the jack finderdriving circuit to bring the finder to rest and operates relay L.Contact ll. connects earth over contacts 222, 12, and wiper FA3 to theright hand winding of relay H, contact 22 opens to release relay A andcontact 13 opens in the allotter homing circuit. Relay H operates andlocks up over its low resistance left hand winding and the highresistance right hand winding of relay CO, the low resistance earthconnection marking the jack engaged to further finders. Contacts h2 and72.3 switch the speaking wires through and contact h4 connects earth tohold relays-LC and KC and to the contact in the arc of wiper FA5 to busythe line to a searching allotter and release relay C. The release ofrelay A opens the circuit of relay B at contact a2 and on the subsequentrelease of relay B relays E and F release. Relay K now being shortcircuited over contact hl releases and releases relay L, and relay D isreleased by the opening of contact cl: The homing circuit for theallotter is now closed and runs from earth over off normal contact onl,contacts Z3, b2, 7'3, all, motor FAM to battery and the allotter israpidly horned its circuit being opened at contact on! in the homeposition.

When the allotter was first taken into use relay SA operated and wasfollowed after a delay period by the operation of relay SB. Contact.s'b-l closes a circuit for relay A of the second allotter which isstarted. Due to. the connection of earth over contact (12 of the firstallotter and the commoned contacts in the arc of wiper FAB the secondallotter is prevented from testing in to a line of the P. B. X. groupafter the seizure of one by the first allotter since its relay C will beshort circuited by the earth in the earlier traced circuit and itcontinues to rotate until its home position is reached or until a freeline in another marked group is found. Relay D (or J if no freeavailable jack finder has been found) in the first allotter will beoperated and relay E in the second allotter is prevented from operatingwhen the first con-, tacts of the group searched by the first allotterare reached by reason of a short circuit extending from earth overcontact saZ, terminals AT and DT, wiper FA1, rectifier R2, contact b1,relay E', contacts d5, 7'5, wiper FAB, commoned terminals GT associatedwith the group concerned, wiper FAQ of the first allotter, contact '5 orcontacts 75 and (15 therein to earth. The second allotter continues inmotion past the group and searches, if necessary in a further markedgroup. When the second allotter leaves its normal posihand this line isbusy,

tion its contacts 0012 open and relay'SA releases and is followed afteran interval by the release of relay SB. Since the starting circuit forthe first allotter depends on relay SA and this relay can only beoperated when both allotters are at normal the first allotter isprevented from making a research until the second allotter has homed.

As soon as the finder started by the first allotter has found thecalling line, relay CS is released if no further call is waiting and atcontact 052 releases relay A of the second allotter. Contact a2 opening,relay B is released and the second allotter homes. If another call hadbeen waiting, relay CS would not have released and the second allotterwould have searched for a free finder in the marked group.

If the last line of 'the group'is reached during the test for a freeline by the first allotter to be started, relay G operates and stopsfurther drive by opening the circuit of motor RAM at contact 'gl. Ifthis line is free; relay C also operates with the result beforedescribed and at contact cl, prevents relay J from operation. If, on theother relay C does not operate but relay J does and at contact lconnects direct earth over contact 123, wiper FA4, terminals ET andBT,c0ntacts s4 and 002 (relay S has not been released since relay CO hasnot been operated), to the bush of the jack. Relay M in the cord circuitis operated but not relay N and the caller receives a busy signal fromthe cord circuit in the manner already described in connection withFig. 1. The operation of relay J releases relay B at contact 7'2 whichin turn releases relay J and the allotter homing circuit is closed. Thesleeve circuit being now opened at contact m1 in the cord circuit, relayS is dependent on relay B and On the release of this relay, relays S,CS, SA, SB and A release if no other call is waiting and the allotterr0- tates to and remains in its home position. If a call in anothergroup: is waiting, relays CS and A will not be released and the releaseof relay J will cause re-operation of relay B and a renewed search bythe allotter.

When the allotter FA is taken into use and relay B is operated, the lefthand winding of relay SS is connected over contacts b6 and 223 to a wireSSW which is earthed periodically. Relay SS operates on the firstearthing on wire SSW after the operation of relay B and locks up overits right hand winding, contacts s8! and b5. Contact s82 prepares acircuit for relay ZZ over wire ZZW which is earthed momentarily afterthe elapse of a prescribed interval from the earthing of wire SSW. If,during this interval the allotter is released, either as a consequenceof its having found a free line and controlled the finder JF to connectthis line to the jack CJ or as a consequence of its not being successfulin its search for afree line and relay B is released, relay ZZ is notoperated. If the allotter is not released within this time relay ZZ isoperated and locked up over contact 22!. Contact 223 disconnects theleft hand Winding of relay SS from wire SSW, contact 225 lights an alarmlamp ZL in a circuit which includes a relay for giving an audible alarm,contact 222 releases relay B and contact 224 prevents relay A fromoperating after the allotter is horned. Relay B releasing, the allotterhomes in the manner previously described. Relay ZZ is released by anattendant investigating the cause of the prolonged holding of theallotter by short circuiting the springs ZJ by means of a plug. Thealarm lamp ZL is extinguished and the audible alarm nated as a whole JFMand FAM.

I claim:-

1. In a telephone system, a line, a second line, a group of findershaving access to said second line, a start circuit for'said finders,means responsive to the establishment of a connection between the firstand second lines for placing a calling condition on the second line,thereby closing said start circuit, means responsive to the closure ofsaid start circuit for starting a finder if one is available, meansefiective if all the finders are busy for transmitting a signal throughthe established connection between the first and second lines, and meansindividual to the first line and responsive to the signal for removingthe calling condition on the second line.

2. In a telephone system, of lines, a plurality of a plurality of groupsgroups of finders corresponding, respectively, to said groups of lines,an allotter common to all said finders, means re 'sponsive to a callingcondition on any line for causing said allotter to search for an idlefinder which corresponds to the group in line is located, and means inthe group which such calling efiective in case said allotter finds allthe finders in such group busy for removing the calling condition fromthe calling line.

3. In a telephone system, a plurality of groups of finders, an allotterhaving access to all said finders, means responsive to a call on a lineaccessible to the finders of a certain group for starting said allottersearching for an idle finder in such group, registering means in theallotter operated responsive to testing of the first finder in suchgroup, registering means in the allotter operated responsive to testingthe last finder in the group only if said first registering means hasbeen operated, and means for stopping the operation of the allotterresponsive to the call contingent on the operation of both registeringmeans and on all finders in the group being found busy.

4. In a telephone system, a line, a plurality of finders having accessto said line, a first allotter common to all said finders, a secondallotter common to all said finders, means responsive to a call on saidline for starting said allotters successively, and means for introducinga predetermined time interval between the starting of the first allotterand the starting of the second allotter.

REGINALD GRIFFITH DIXON.

